Elsewhere I have tried to show that unity within the fellowship is the major theme of Philippians. Paul sees disunity as a sin that destroys the church's witness and renders it impotent. I find it interesting and instructive that Paul's second missionary journey -- during which the Philippian church was founded by Paul -- was itself born out of heartbreaking division. The great partnership of Paul and Barnabas had come to an unhappy end. Of course, God used it for good, as he always does. But it is surely no wonder that a church in which Paul saw major divisions should have concerned him.
Notice something else. During Paul's second journey he sought and received the guidance of God in the form of a vision. However, Paul takes no direct action on his own. He submits the vision to his team, and only when unanimity has been reached do they set out for Europe. Paul's cautious reaction to the divine vision suggests to me a sensitivity to unity and cooperation that perhaps was missing at the beginning of the trip.
Unity is not really a choice but a command. Just read Phil. 1:27-30. And the extent to which we obey probably says more about us and our Christianity than anything else.